If you are booting into a clean Workbench AmigaOS 3, then it may be very fast, but if you add all the patches, hacks and applications that wouldn't bring even half of the usability of AmigaOS 4 (fully working connected TCP/IP stack, Dock, 32-bit icons, virtual memory, contextal menus, visual prefs, memory protection etc..) it will boot much slower, if booting at all.
Still advertising memory protection on AmigaOS4?
Let's say it again: there's *NO* memory protection on AmigaOS4 (nor AROS, MorphOS).
Both MorphOS and OS4 come with limited protection in some cases, but it's nothing to do with real memory protection. So please stop including it as an AmigaOS4 feature.